This invention relates to a method of reducing the corrosion of a carbon steel reboiler in which a reboiler fluid containing nitrogen trichloride is heated to decompose the nitrogen trichloride. In particular, it relates to the addition to the reboiler of about 1 to about 100 parts ppm of a source of iodine.
When brine is electrolyzed to produce caustic and chlorine, ammonia in the brine can result in the production of nitrogen trichloride, NCl.sub.3. Nitrogen trichloride is an explosive gas and it is essential that it be removed from the chlorine before its concentration builds up to explosive levels. Its removal from the chlorine is accomplished by contacting the chlorine with a reboiler fluid that absorbs nitrogen trichloride. The reboiler fluid containing the absorbed nitrogen trichloride is heated in the reboiler to a temperature in the range of 40.degree.-60.degree. C., which results in the decomposition of the nitrogen trichloride into nitrogen and chlorine, which is recycled.
While this process is effective at destroying nitrogen trichloride, it rapidly corrodes carbon steel reboilers. The reboilers are corroded so rapidly that it is necessary to replace them at considerable expense every three or four months. The use of reboilers made of less corrosive materials, such as Hastelloy, a nickel-iron alloy, has been considered, but such reboilers are far more expensive than carbon steel reboilers. Since the reboiler fluid contains virtually no water, the source of the corrosion has been a mystery and an effective anti-corrosion agent has not been found.